Permanently rotating free aerostat mobile in radial translation relative to ambient air

ABSTRACT

The invention concerns a free lighter-than-air aerostat comprising a structure (1, 3, 4, 5) symmetrical relative to a main axis (2), at least one main sealed pressurized chamber (16), one or several particle emitting thrusters (8), adapted to drive the aerostat in rotation in one direction about the main axis (2), one or several moving flaps (9) adapted to be set either in an active state wherein they brake the aerostat rotation, or in an inoperative state wherein they offer no substantial resistance to the aerostat rotation, and on-board control means (19) adapted to control the thrusters (8) and the flaps (9) to drive the aerostat in permanent rotation about the main axis (2), and in translation perpendicular to the main axis (2).

The invention relates to a lighter-than-air aerostat, of the typecomprising at least one main chamber closed in a sealed manner, with aconstant volume, which is pressurised by a gas lighter than air, such asto permit rising and flight of the aerostat. Throughout the presentapplication, “aerostat” means any vehicle lighter than air, and“geostationary” means the fact that an aerostat remains at leastsubstantially vertical relative to a point which is fixed in relation tothe ground.

So-called free aerostats are those which are not connected mechanicallyto the ground, unlike captive aerostats. Conventional free balloons havethe disadvantage that they drift, in particular horizontally, inrelation to the ground, according to the winds, without any possibilityof controlling their position or their path. Captive balloons do nothave this disadvantage, and are at least substantially geostationary.However, they require at least one cable for connection to the ground,which is heavy and triangulated, is a source of danger for air traffic,and in practice prevents selection of this technology for aerostatswhich are designed to fly at a high altitude, and in particular forstratospheric aerostats.

If it is required to be able to pilot the horizontal position (i.e. theposition relative to the ground) and/or the horizontal path of a freeaerostat for a long period of time (ranging from a few months to severalyears), it is out of the question to have on board consumable energy.With solar energy, the problem must be faced of the weight of thecollector devices and of the means of storage, taking into accountfirstly the fact that the efficiency of the electric motors (inparticular the ratio of the thrust to the power consumed) is too low,and secondly the night flight which must be assured.

In addition, since free aerostats are extremely sensitive tometerological conditions and horizontal winds, a very large inflatedvolume must be provided, in order to be able to carry on-boardposition-correction motors, the power of which makes it possible tocompensate for the horizontal aerodynamic drag.

In particular, it is known that a stratospheric geostationary balloonwould require a minimum volume of approximately 350,000 m³, and aminimum weight of approximately 10 tonnes, in order to be able to carrymotors making it possible to control its horizontal position and/or itshorizontal path at a stratospheric altitude, as well as a useful loadsuch as a telecommunications system. Dimensions of this type represent asubstantial volume, and a significant risk for air traffic, and for thepopulations, if the balloon falls or is destroyed. In addition, thesedimensions cause problems of practical production and launching. Inaddition, the assembly would have a high cost, for relatively lowreliability.

However, long-lasting stratospheric missions would permit scientificstudy of the upper atmosphere, observation of the earth, improvement oftelecommunications, etc. In particular, it is desirable to be able tohave at a stratospheric altitude numerous devices which can act asactive or passive relays for hertzian connections, for example fortelecommunications satellites (mobile telephony, radio, television, datanetworks, etc) or localisation satellites (GPS, Argos systems, etc).

Therefore, there is a need to be able to place vehicles at a highatmospheric altitude, and in particular at a stratospheric altitude, theposition or displacements of which relative to the ground, in particularhorizontally, can be controlled automatically or from the ground,without a human pilot on board, for a duration which can be between afew days and several years.

The object of the invention is thus to eliminate these disadvantages, byproviding a free vehicle which is designed for a high atmosphericaltitude, and in particular a stratospheric altitude, and of which thehorizontal position (in longitude and latitude) and/or the horizontaldisplacements relative to the ground can be controlled automatically,autonomously or from the ground, for a substantial period of time.

In particular, the object of the invention is to solve the problem posedby the energy necessary for motorisation, which makes it possible tomaintain the horizontal position and/or to follow a horizontal path.

More particularly, the object of the invention is to provide a vehicleof this type, formed from an aerostat which is designed for a highatmospheric altitude, and in particular a stratospheric altitude, thevolume of which is limited, and in particular is between 10 m³ and10,000 m³, for example approximately 2,000 m³, for a weight of between10 kg and 500 kg, and in particular between approximately 50 kg and 200kg.

In addition, the object of the invention is to provide an aerostat whichis particularly suitable for acting as an active and/or passive relayfor transmission of data by hertzian means, in particular in the fieldof hyperfrequencies.

For this purpose, the invention relates to a lighter-than-air aerostat,comprising:

a strengthening structure, which defines a shape which is symmetricalrelative to a main axis;

at least one main chamber closed in a sealed manner, which is integralwith the said structure, and is pressurised by a gas which is lighterthan air, such as to permit flight of the aerostat;

means for driving the aerostat comprising:

one or a plurality of particle-emission propulsion units supported bythe said structure, which are regularly distributed around the mainaxis, and are designed to be able to drive the aerostat in rotation inone direction around the main axis, and to be able to be controlled froman active state to an inactive state and vice-versa, at least once foreach rotation of the aerostat around the main axis;

one or a plurality of mobile flaps, which are supported by the saidstructure outside the main chamber, are distributed regularly around themain axis, and are designed to be able to be controlled at least oncefor each rotation of the aerostat around the main axis, from an activestate, in which they brake the rotation of the aerostat, whilst exertingaerodynamic thrust which tends to displace the aerostat in translationperpendicularly relative to the main axis, to an inactive state, inwhich they do not offer any substantial resistance to the rotation ofthe aerostat, and vice versa; and

on-board control means, which are designed to control the propulsionunits and the flaps in order to

drive the aerostat in continuous rotation around the main axis; and

drive the aerostat in translation, with at least one component which isperpendicular to the main axis, relative to the volume of air in whichit moves.

“Translation with at least one component perpendicular to the main axis”means movement of translation in a direction of translation which has acomponent which is non-zero, according to the direction which is radialrelative to the main axis, i.e. which is not parallel to the main axis.Preferably, advantageously and according to the invention, the means fordriving the aerostat are designed to drive the aerostat in translationin a direction of translation which is at least substantially radialrelative to the main axis, i.e. which is perpendicular to the main axis.

Advantageously, an aerostat according to the invention has an overallaxial dimension parallel to the main axis which is smaller than that ofits overall radial dimension perpendicular to the main axis. Preferably,and according to the invention, it has a general outer shape which isglobally symmetrical in revolution around the main axis, and inparticular is globally lenticular.

In one embodiment, and according to the invention, the aerostat has anoverall radius of between 5 m and 50 m, and in particular approximately15 m, and an overall axial height of between 1 m and 20 m, and inparticular approximately 10 m.

Advantageously and according to the invention, the aerostat comprises atleast one ionic actuator and/or at least one air pulsation unit, as aparticle-emission propulsion unit, these particles then beingrespectively ions and/or gas molecules.

Advantageously and according to the invention, each of the propulsionunits is associated with a peripheral portion of the said strengtheningstructure which is furthest away from the main axis, and is disposedsuch as to exert a drive force which is at least substantiallytangential. Similarly, advantageously and according to the invention,each of the flaps is associated with a peripheral portion of the saidstructure which is furthest away from the main axis, and is disposedsuch as to exert a force which is at least substantially tangential.

Advantageously and according to the invention, each mobile flap extendsat least substantially radially, and is mobile parallel to the mainaxis, between a position retracted in a flap compartment, in which itdoes not interfere with the relative current of air obtained from thedisplacements of the aerostat relative to the volume of air in which theaerostat is placed, and an extended position, in which it interfereswith the current of air, and tends to brake the rotation of the aerostataround the main axis, whilst exerting reactive aerodynamic thrust, whichdrives the aerostat in translation.

In addition, advantageously and according to the invention, the on-boardcontrol means are designed such that, in a first angular sector, whichextends from one side in a radial direction which is perpendicular tothe main axis, and fixed in relation to the corresponding wind(independently of the rotation of the aerostat around the main axis),each propulsion unit is in the active state, and each flap is in theinactive state, whereas in a second angular sector, which extends to theother side of this radial direction, each propulsion unit is in theinactive state, and each flap is in the active state, such that theaerostat is driven in translation relative to the corresponding wind, atleast substantially according to this radial direction. Preferably andaccording to the invention, the drive means are designed to be able todrive the aerostat in rotation around the main axis at a speed ω whichis at least substantially constant, of between 1 rd/s and 100 rd/s, andin particular approximately 2π rd/s. In addition, advantageouslyaccording to the invention, each propulsion unit and each flap isdesigned to be able to be controlled from the inactive state to theactive state, and from the active state to the inactive state, in aperiod of less than 2π/4ω, ω being the speed of rotation of the aerostatexpressed in radians per second.

Advantageously, an aerostat according to the invention additionallycomprises means for location of the position of the main axis relativeto a reference point which is fixed in relation to the ground, and meansfor location relative to this same fixed reference point for the angularposition (in rotation) of the structure relative to the main axis, andthe said control means comprise calculation means which are designed todetermine the control signals to be applied to each propulsion unit andto each flap, according to signals emitted by these location means, andin accordance with a predetermined instruction signal for the horizontalposition and/or the horizontal path of the main axis, relative to thefixed reference point.

Advantageously, the aerostat according to the invention is characterisedin that it comprises at least one flexible outer envelope, whichdelimits at least one main chamber which is sealed against gases, and ispressurised by a gas lighter than air, and in that each of the mobileflaps is disposed outside this outer envelope. Similarly, eachpropulsion unit is secured to the structure inside the envelope, and hasa particle-ejection nozzle, which passes through the envelope in asealed manner, in order to emit the particles outside the envelope.

Advantageously and according to the invention, the gas consists ofhelium, and the volume of the main chamber is designed to permitstratospheric flight of the aerostat.

Advantageously and according to the invention, the aerostat isadditionally characterised in that the structure comprises a peripheraltoric balloon, which is sealed against gases, and is over-pressured by agas lighter than air, to a pressure greater than that of the mainchamber, in that it comprises the same number of propulsion units asflaps, and in that it comprises support parts which are secured to thisballoon, and are regularly distributed around the main axis, eachsupport part supporting at least one propulsion unit and/or at least onemobile flap.

In one embodiment, and according to the invention, the structurecomprises:

a rigid, globally cylindrical hollow/central core, which can enclose theelectronic and/or computer and/or telecommunications and/or energystorage equipment, and/or equipment of an on-board mission;

an over-pressurised peripheral toric balloon;

support parts which are secured to the peripheral toric balloon, andsupport the propulsion unit(s) and the mobile flap(s);

connection means, which connect the central core and the support parts;and

an outer envelope, which surrounds and/or completes the volume delimitedby the peripheral toric balloon and the central core, in order tocircumscribe at least one pressurised, sealed main chamber.

In addition, an aerostat according to the invention comprises anon-board energy source, which is designed to assure the energy supply atleast of each propulsion unit. Preferably and according to theinvention, this energy source is also designed to assure the energysupply of drive units for manoeuvring the flaps, as well as the energysupply of the control means, the location means, and the on-boardmission, i.e. of the aerostat as a whole, which is then totallyautonomous from the point of view of its energy supply.

Advantageously and according to the invention, the energy sourcecomprises:

photovoltaic solar cells which are disposed on at least one uppersurface portion of the aerostat; and

means for storage of electrical energy.

The electrical energy storage means can consist of rechargeableaccumulators and/or a fuel cell/fuel cells. Their capacity is determinedsuch as to permit night flight.

The invention thus makes it possible to obtain a free aerostat which canbe launched to a high altitude, and in particular to a stratosphericaltitude, and of which the horizontal position and/or the horizontalpath can be controlled automatically for a long period of time. Inparticular, it should be noted that the drive means for the aerostatmake it possible to use for displacement in horizontal translation ofthe aerostat, most of the kinetic energy of the particles emitted by thepropulsion units, which are themselves displaced relative to the volumeof air (by the rotation of the aerostat) at a speed which is very muchhigher than the speed of horizontal translation of the aerostat. Thepropulsion power created by each propulsion unit is greatly increasedcompared with the case of an aerostat which is not driven in continuousrotation. For the same resulting force of propulsion in horizontaltranslation, the invention makes it possible to reduce considerably theenergy consumption, and thus the weight of the energy source (solarcells, storage cells, etc), which is a determining factor within thecontext of production of a long-lasting free aerostat, which isgeostationary, or mobile according to a predetermined path.

The invention also relates to an aerostat which is characterised inassociation by some or all of the characteristics described previouslyor hereinafter.

Other characteristics, objectives and advantages of the invention willbecome apparent from reading the following description, provided withreference to the attached drawings, in which:

FIG. 1 is a view in axial cross-section (left-hand part) and inelevation (right-hand part) of an aerostat according to an embodiment ofthe invention;

FIG. 2 is a perspective view of the aerostat in FIG. 1;

FIG. 3 is a partially cut-out plan view from below of the aerostat inFIG. 1;

FIG. 4 is a plan view from above of the aerostat in FIG. 1; and

FIG. 5 is a skeleton drawing illustrating the functioning of the drivemeans of an aerostat according to the invention.

The aerostat shown in the Figures comprises a strengthening structure 1,3, 4, 5, consisting of a central core 1, which is globally cylindricalin revolution around a main axis 2; an over-pressurised peripheral toricballoon 3, which is symmetrical in revolution around the main axis 2;support parts 4 which are secured to the peripheral toric balloon 3; andconnection units 5, which connect the central core 1 and the supportparts 4, preferably in the form of flexible cables. These connectionunits 5 are designed such that in the flight position, the peripheraltoric balloon 3 is centred on the main axis 2. In fact, since theaerostat is driven in continuous rotation, if these connections 5consist of cables, the latter are stretched tight by centripetal force.

This strengthening structure is balanced in relation to the main axis 2.The same applies to the aerostat as a whole. This balancing is obtainedby regular distribution of the weights around the axis 2, and, ifnecessary, by additional balancing weights positioned after completionof assembly of the aerostat. The strengthening structure and theaerostat as a whole (with the exception of the units which areincorporated inside the central core 1) have angular symmetry around themain axis 2, i.e. they can be considered to be obtained fromjuxtaposition around the main axis 2 of a plurality of similar angularsectors.

In the embodiment shown, the central core 1, the toric balloon 3, andthe connection units 5 have symmetry relative to a median plane which isperpendicular to the main axis 2, which intersects diametrically thetransverse straight cross-section of the toric balloon 3. However, thissymmetry is not necessary, and the aerostat according to the inventioncan have an asymmetrical axial cross-section.

The support parts 4 are secured to the peripheral toric balloon 3, forexample by being glued or welded on the interior, i.e. on the main axis2 side. Each support part 4 has the general shape of an arc of a portionof a torus, with a shape corresponding to that of the peripheral toricballoon 3 to which it is attached. Each support part 4 is connected tothe central core 1, for example by four cables 5, i.e. two upper cables5 a and two lower cables 5 b, which are secured rigidly in the vicinityof each of the ends of the support part 4. The cables 5 are securedfirstly to the corresponding support part 4, and secondly to the centralcore 1, by means of any appropriate rigid securing device (flange, cableclamp, looping the end of the cable through a ring, etc). The toricballoon 5 is integral in rotation with the central core 1.

The central core 1 is globally cylindrical in revolution around the mainaxis 2, it is rigid, hollow, and is designed to be able to contain theelectronic and/or computer and/or telecommunications and/orenergy-storage equipment, and/or equipment of an on-board mission. Inthe embodiment shown, the central core 1 comprises a base 6 and a cover7. It should nevertheless be noted that this base 6 and this cover 7 arenot essential, and the various items of equipment can be secureddirectly to the cylindrical walls inside the core 1. Preferably, thewalls which form the cylindrical central core 1 are perforated, andconsist of a rigid light material, for example a compound based oncarbon fibres, such as to be as light as possible. The same applies tothe support parts 4.

The various support parts 4 are regularly distributed around the mainaxis 2. Thus, the aerostat can comprise two diametrically oppositesupport parts 4. In the preferential embodiment shown, the aerostatcomprises three support parts 4, which are regularly distributed at 120°C. from one another around the axis 2.

Each support part 4 supports a particle-emission propulsion unit 8and/or a mobile flap 9.

According to the most basic embodiment of the aerostat according to theinvention, the latter comprises two diametrically opposite support parts4, one of which supports a propulsion unit 8, whereas the other supportsa mobile flap 9. In the preferred embodiment shown, advantageously andaccording to the invention, each support part 4 supports a propulsionunit 8 and a mobile flap 9, and the aerostat comprises a plurality ofsupport parts 4, and in particular more than two support parts 4, aplurality of propulsion units 8, and in particular more than twopropulsion units 8, and a plurality of mobile flaps 9, and in particularmore than two mobile flaps 9.

The propulsion units 8 consist of ionic actuators and/or air pulsationunits. An ionic motor with a corona effect can for example be used asthe ionic actuator. An axial air compressor can be used as the airpulsation unit. Particle-emission propulsion units of this type arealready known.

Each propulsion unit 8 can be supplied with atmospheric air from thecompartment 11 of the flap 9, and in particular the one which is securedto the same support part 4. For this purpose, each flap compartment 11has an air intake aperture 27 upstream from the flap 9, and a pipe 26for connection to the propulsion unit 8, such that the air entersupstream from the flap 9 into the compartment 11, and is supplied to thepropulsion unit 8 by the pipe 26. The air is captured in the compartment11 when the flap 9 is deployed, and is stored in this compartment 11until it is used to supply the propulsion unit 8 when the latter isactivated.

Each propulsion unit 8 is secured to a support part 4 by any appropriatesecuring means (flange, collar, welding, etc), and has a nozzle 10 forejection of particles, which has a generally cylindrical shape. All thepropulsion units 8 of the aerostat are oriented in the same direction,i.e. with their ejection nozzles 10 oriented in order to drive theaerostat in rotation around its main axis 2 in the same direction. Eachpropulsion unit 8 is secured to the support part 4, such that itsejection nozzle 10 extends at least substantially in the direction whichis perpendicular to the bisector of the angular sector which is definedby the arc of the portion of a torus formed by the corresponding supportpart 4. Thus, each propulsion unit 8 is secured to the support part 4,such as to exert a drive force which is at least substantiallytangential (relative to the peripheral toric balloon 3, at its point ofintersection with the bisector of the angular sector defined by thesupport part 4).

In addition, the aerostat is designed to fly with the main axis 2extending at least substantially vertically, with the median planeperpendicular to the axis 2, which extends at least substantiallyhorizontally, as shown in the Figures. In order to decrease as much aspossible the centre of gravity of the aerostat and to assure itshorizontal stability, the propulsion units 8 are preferably disposed ina position which is as low as possible, on the lower part of the supportparts 4, beneath the lower cables 5 b, as shown in the Figures.

Each mobile flap 9 is integrated and supported in a compartment 11,which itself is rendered integral with one of the support parts 4, forexample by means of a tube or connection bars 12. Each compartment 11,and the connection elements 12 which make it possible to attach thecompartment to the support part 4, consist of a rigid material, forexample a compound based on carbon fibres. Each flap 9 is fitted in thecompartment 11 such as to extend at least substantially in an axialplane, i.e. in a plane which contains the main axis 2, and in adirection which is radial relative to this main axis 2. Each compartment11 extends globally inside the space which is contained between theperipheral toric balloon 3 and the central core 1, as far as possiblefrom the main axis 2. In the embodiment shown, each compartment 11comprises a single flap 9, which is fitted such as to rotate around ashaft 13 which is at right angles to the main axis 2, and is supportedby the compartment 11. The size of the compartment 11 is such that theflap 9 can be completely retracted and integrated in this compartment11, in the inactive state. In addition, the flap 9 is fitted relative tothe compartment 11 such that it can be deployed in the active state, inwhich it brakes the rotation of the aerostat around the main axis 2,whilst exerting aerodynamic thrust, which tends to displace the aerostatin translation, perpendicularly to the main axis 2. In the embodimentshown, each compartment 11 is open towards the top, and the mobile flap9 is fitted such that it can be deployed upwards, vertically by rotationaround the shaft 13, by means of an electric motor 14, which isincorporated inside the compartment 11, on the shaft 13.

As a variant, it would also be possible to fit the flaps 9 and thecorresponding compartments 11 such that the flaps are deployeddownwards. As a variant, each compartment 11 could also be secured to asupport part 4 with two flaps 9 which are deployed respectively oneupwards and the other downwards, in order to assure braking of therotation on both sides of the median horizontal plane. The flaps canalso be mobile in translation rather than in rotation, or according to amovement which combines rotation(s) and translation(s). In addition,each of the flaps 9 can also be profiled in the manner of an air brake.In fact, the function of these flaps is to provide maximum aerodynamicthrust in the active state, for a minimum weight of the assemblyconsisting of the flap 9, compartment 11, motor 14, and kinematiccontrol mechanism 13.

The aerostat additionally comprises a flexible outer envelope 15, whichfor example consists of MYLAR®, which delimits a main chamber 16 whichis sealed against gases, which, as well as the toric balloon 3, ispressurised by a gas which is lighter than air, for example helium. Thisenvelope 15 extends around the peripheral toric balloon 3 and towardsthe main axis 2, above and below the central core 1.

Each of the ejection nozzles 10 of the propulsion units 8 passes throughthe envelope 15 in a sealed manner, such that the particles which areemitted by the propulsion units 8 are ejected outside the main chamber16. Similarly, each of the mobile flaps 9 is disposed outside the outerenvelope 15, the latter being interrupted and open at the level of theperipheral edges 22 of the aperture of the compartments 11 of the flaps.

The upper surface 17 of the upper portion 24 of the envelope 15 iscovered with a set of photovoltaic solar cells 21, which can extend asfar as the flap compartment 11, or even as far as the extreme peripheralpart of the envelope 15, around the apertures of the compartments 11, ifnecessary. This set of solar cells 21 is connected electrically insidethe central core 1, by appropriate electrical conductors, which passthrough the envelope 15 in a sealed manner, and are connected toelectrical energy storage means 18, formed by an accumulator battery ora fuel cell (for example such as those which were used in the spaceprogrammes (APOLLO, SPACE SHUTTLE, etc)). In this case also, storagemeans 18 which have the greatest capacity for the lowest weight arepreferred. These electrical energy storage means 18 are incorporatedinside the central core 1, as are the electronic and/or computer controlmeans 19 for the propulsion units 8 and the flaps 9.

Electrical conductors 20 connect these control means 19 electricallyinside the central core 1, firstly to each of the propulsion units 8,and secondly to each drive motor 14 for the mobile flaps 9, through thewall of the compartment 11, through which these conductors 20 pass in asealed manner. The conductors 20 are for example supported by at leastone of the cables 5 for connection of the support parts 4 to the centralcore 1, and preferably a lower connection cable 5 b.

The aerostat according to the invention thus has a general outer shape(i.e. the outer contour defined by the outer envelope 15) which isglobally symmetrical in revolution around the main axis 2. This shape isalso globally lenticular, and its axial dimension parallel to the mainaxis 2 is smaller than its overall radial dimension perpendicular to themain axis 2. In addition, the shapes of the aerostat according to theinvention are defined such as to minimise the coefficient of horizontalaerodynamic friction Cx (perpendicular to the axis 2). Advantageously,the aerostat according to the invention has an overall diameter ofbetween 5 m and 100 m, and in particular approximately 30 m, and anoverall axial height of between 1 m and 20 m, and in particularapproximately 10 m, corresponding to the axial height of the centralcore 1. The diameter of the central core 1 is as small as possible,taking into account the volume thus delimited, which is designed tocontain the electrical energy storage means 19 and the various items ofelectronic and computer equipment.

The volume of the main chamber 16 which is sealed against gases isdesigned to permit flight of the aerostat, in particular at astratospheric altitude. This main chamber 16 can consist of a singlevolume or of several volumes which are imbricated and/or juxtaposed. Itcan thus be compartmentalised, and/or contain gas cells.

For example, the main chamber 16 is pressurised at an over-pressure(relative to the atmospheric pressure of the required flight altitude)of approximately 300 Pa, whereas the peripheral toric balloon 3 ispressurised at an over-pressure (relative to the atmospheric pressure ofthe required flight altitude) of approximately 500 Pa, i.e. it isover-pressurised relative to the main chamber 16 by an over-pressure ofapproximately 200 Pa. Thus, the peripheral toric balloon 3 establishesand maintains the general lenticular shape of the aerostat.

In addition, it should be noted that the aerostat has an apparentsurface area seen from the ground, which is extremely large in relationto its total weight. Thus, the aerostat according to the invention canincorporate a reflective radio-electric surface, which for example is ofthe type which makes it possible to reflect towards the groundradio-electric signals obtained from the ground. For example, the innersurface 23 which is oriented downwards, of the upper portion 24 of theouter envelope 15, can be metallised, the lower portion 25 of the outerenvelope 15 being constituted from materials which areradio-electrically transparent. Thus, the upper portion 24 of theenvelope 15 has a concave reflective surface which is oriented towardsthe ground. As a variant, there can also be incorporated a reflectivesurface of this type with an appropriate shape, and more generally anytype of active or passive radio-communication antenna, inside theaerostat itself, in the main chamber 16 between the toric balloon 3 andthe central core 1.

The aerostat according to the invention also comprises at least onereceiver of the GPS (GLOBAL POSITIONING SYSTEM) or DORIS type, etc, orany other location device (gyroscope, telemetry means, accelerationmeter, magnetometer, etc) which makes it possible to locate the positionof the main axis 2 in relation to a reference point which is fixed,relative firstly to the ground, and secondly to the angular position ofthe aerostat in its rotation around the main axis 2.

According to an advantageous embodiment of the invention, the aerostatcomprises a GPS receiver, which makes it possible to locate its positionwith accuracy of approximately 100 m relative to the ground. Inaddition, in order to locate the angular position of rotation of theaerostat around the main axis 2, the latter incorporates a magnetometer,the accuracy of which is approximately a degree, and which can begraduated according to the local magnetic field. This GPS receiver andthis magnetometer are supported inside the central core 1.

As the GPS receiver, use can be made for example of a GPS TANS VECTORreceiver for determination of altitude and position, sold by the companyTRIMBLE NAVIGATION (Hampshire, England). The antennae of the receiverare located and secured either on the periphery of the core 1, or on thesupport parts 4, in the vicinity of the toric balloon 3, or on the toricballoon 3 at the extreme periphery of the aerostat.

The aerostat also advantageously comprises means fortransmission/reception which permit communication with the ground, inparticular for programming of its horizontal position and/or itshorizontal path. It also incorporates computer calculation means, which,from a predetermined instruction position (programmed in advance orreceived from the ground) and from the position determined by thelocation means, make it possible to determine a horizontal translationcourse. This course can be simply the straight line which passes throughthe instruction position and through the position located, optionallytaking into account the relative wind, i.e. drift. A computer navigationsystem of this type is known, and does not need to be described indetail.

The on-board control means 19 are designed such that, in a first angularsector 28, which extends from one side in a radial direction Da, whichis perpendicular to the main axis 2, and is fixed in relation to therelative wind, (independently from the rotation of the aerostat aroundthe main axis 2), corresponding to the horizontal translation course tobe imparted to the aerostat, each propulsion unit 8 is in the activestate, and each flap 9 is in the inactive state, whereas in a secondangular sector 29 which extends from the other side of this radialdirection Da, each propulsion unit 8 is in the inactive state, and eachflap 9 is in the active state, such that the aerostat is driven intranslation in relation to the relative wind, according to this radialdirection Da.

The first angular sector 28 and the second angular sector 29 arepreferably bisectors of the plane angle defined by the direction Da,i.e. a straight line perpendicular to Da is the bisector of each ofthese angular sectors 28, 29. In addition, these angular sectors 28, 29preferably have at least substantially the same angular value lower than180°, and are symmetrical with one another relative to the direction Da.

The propulsion units 8 and the flaps 9 are designed to be able to becontrolled from the inactive state to the active state, and from theactive state to the inactive state in a period of less than 2π/4ω, ωbeing the speed of rotation of the aerostat expressed in radians persecond, which is advantageously between 1 rd/s and 100 rd/s, and inparticular approximately 2π rd/s.

The diagram in FIG. 5 illustrates the functioning of an aerostataccording to the invention, in the case of a single propulsion unit 8and a single mobile flap 9, which are radially opposite relative to themain axis 2 (this hypothesis being used for reasons of simplification ofthe calculations). Let us consider a propulsion unit 8 which projectsparticles (ions, atoms, etc) at a relative speed V1 which is assumed tobe homogenous, with a mass flow D (in kg/s), and which induces apropulsion force Fa applied to the centre of gravity G.

A is the point of connection of the propulsion unit 8, Va is the speedof this propulsion unit 8, G is the centre of gravity, which is assumedto be located on the main axis of rotation 2, and Vg is the speed of thecentre of gravity G in relation to the volume of air.

The particules are emitted in a direction which is at leastsubstantially opposite that of the speed vector {right arrow over (Vg)}.As a first approximation, the effect of the propulsion unit 8 can bebroken down into a force Fa which is applied to the Centre of gravity,and moment Ca around the axis of rotation, such that:

Fa=V1.D

Ca=V1.D.R, R being the distance from A to G

Let us now consider the presence of a mobile flap 9 which is centred ata point B which is spaced from the axis 2 and from G by a distance R′,R′<R, and is displaced at a speed Vv:${Vv} = {{Vg} + {\frac{R^{\prime}}{R} \cdot {Va}}}$

The action of this flap 9 takes the form of a thrust force Fv and momentCv around the axis of rotation 2.

Cv=−Fv.R′

Let it be assumed that the extension of the flap 9 is made to coincidewith the thrust of the radially opposite propulsion unit 8 (on theassumption that the mobile flap 9 can be extended and withdrawninfinitely quickly).

It should be noted that the effect of the drag forces (apart from thosecaused by the flap 9) is not necessarily located on the axis of rotation2 (owing to the rotation of the aerostat), and can thus induce anaerodynamic drag moment. In order to simplify the calculation, it isassumed that this moment is negligible.

The on-board computer controls the surface of extension of the flap 9,so that the global average angular acceleration is zero (the speed ofrotation of the aerostat remaining at least substantially constant):

Ca+Cv=0

Fa.R−Fv.R′=0 ${Fv} = {\frac{R}{R^{\prime}} \cdot {Fa}}$

The global thrust force Fp is therefore equal to:${Fp} = {{{Fv} + {Fa}} = {{Fa} \cdot \left\lbrack {1 + \frac{R}{R^{\prime}}} \right\rbrack}}$

The control means 19 control each propulsion unit 8 such that the forceexerted by the propulsion unit 8 is on average oriented parallel to therequired direction of advance Da. Similarly, the control means 19control each flap 9 such that the force exerted by the flap 9 is onaverage oriented parallel to the required direction of advance Da. Forthis purpose, it is sufficient for the duration of the transition fromthe inactive state to the active state of the propulsion unit 8, or ofthe flap 9, to be the same as that of the transition from the activestate to the inactive state, and for the path described by thepropulsion unit 8 or the flap 9 in the active state to be symmetricalrelative to the straight line which is perpendicular to the direction ofadvance Da and to the main axis 2.

Preferably, the angular position from which a flap 9 begins to beactivated is fixed in relation to the required direction of advance Da,and is aligned radially with the angular position, which is fixed inrelation to the required direction of advance Da, from which apropulsion unit 8 begins to be activated. Similarly, the angularposition which is fixed in relation to the required direction of advanceDa, from which a flap 9 ceases to be activated, is aligned radially withthe angular position, which is fixed in relation to the requireddirection of advance Da, of a propulsion unit 8, from which it iscompletely inactive. Thus, FIG. 4 shows the straight line Di whichrepresents the angular position from which a flap 9 begins to bedeployed (active), and a propulsion unit 8, which is opposite inrelation to the axis 2, begins to be activated, and the straight line Dfrepresenting the angular position from which a flap 9 ceases to becompletely retracted (inactive), and a propulsion unit 8 is completelyinactive. These two straight lines Di, Df form between them an anglewhich represents the angular course in which the flap 9 and a propulsionunit 8 opposite it are active. The value which is equal to half thisangle is known as αmax. The direction of advance Da is a bisector of Diand Df. The straight lines Di and Df define between them the said firstangular sector 28 and the second angular sector 29.

Each propulsion unit 8 is activated for a portion of the period ofrotation, and the direction of thrust is not always perfectly alignedwith the speed vector, thus inducing a loss of efficiency which can betranslated in terms of output r. If a propulsion unit 8 and a flap 9 areactivated only when the loss of aim of the thrust force Fp is smallerthan the angle αmax, the output r is:$r = {{\frac{1}{2\quad \alpha \quad \max} \cdot {\int_{{- \alpha}\quad \max}^{{+ \alpha}\quad \max}{\cos \quad {\alpha \cdot {\alpha}}}}} = \frac{\sin \quad \alpha \quad \max}{\alpha \quad \max}}$

Finally, the global gain factor γ of the propulsion of the aerostataccording to the invention in relation to a fixed propulsion unit is:$\gamma = {r \cdot \left\lbrack {1 + \frac{R^{\prime}}{R}} \right\rbrack}$

It should be noted that for αmax=40°, r≅0.92.

The gain γ makes it possible to reduce the power, and therefore theweight of each propulsion unit 8 in relation to the requirement forthrust force.

In the case of a non-rotary conventional airship (according to the priorstate of the art) with propulsion units, the kinetic energy of theparticles emitted by the propulsion units (operated at a speed which isconventionally approximately a few hundred meters per second) istransmitted only at a low rate to the airship, the speed of which isrelatively low (typically 10 m/s). After being ejected, the particlescontinue to be driven at a high speed which corresponds to unusedkinetic energy.

In the case of the aerostat according to the invention, the propulsionunit 8 is itself driven at a high speed (lower than the speed ofejection of the particles, but very much higher than the speed oftranslation of the aerostat), in a direction opposite of that ofejection of the particles. Once they have been ejected, the latter aredriven at a speed which is far lower than that which they would have hadif the propulsion unit 8 had been immobile, and this can therefore beconsidered as better use of the propulsion energy.

More directly, since the power of a force applied at a given point isequal to the product of this force times the speed of this point, thepower of propulsion developed by the propulsion unit 8 is far greater inthe case of an aerostat according to the invention than in the case of aconventional airship. As a result, in particular, an aerostat accordingto the invention can be supplied entirely by solar energy, and can thusbe kept in a geostationary position in the upper atmosphere.

By way of example, with an aerostat according to the invention, thefollowing can be applicable:

radius R of the aerostat: 15 m

height H of the aerostat at the level of the main axis 2 (overall axialdimension): 10 m

volume at an altitude of 21 km: 2200 m³

outer surface area: 1700 m²

weight: 150 kg

maximum speed of translation in relation to the relative wind: 150 km/h

electrical power consumed: 20 kW

Vg=10 m/s ; ω=2π rad/s ; αmax=40°; r=92%; Va=ωR=94 m/s; R′=10 m; Vv=53m/s; γ=0.92×(1+15/10)≈2.3.

The electronic and/or computer control means 19 make it possible topilot the aerostat according to the invention in accordance with controllogic which makes it possible to control its position and/or path.Control means of this type are known. For example, use can be made ofcontrol means such as those described in the publication “THE PRONAOSPROJECT: DESIGN, DEVELOPMENT AND IN-FLIGHT RESULTS” F. BUISSON et al,IAF-97, Turin, Jun. 10, 1997.

In addition, the stable horizontal position of the aerostat is assuredpassively, since the centre of gravity G is below the median horizontalplane. Any deflection from the stable horizontal position will thus giverise to a moment of return which is proportional to the sine of theangle of deflection.

In addition, in the presence of a quasi-horizontal relative wind, theaerostat according to the invention acts in the manner of an aircraftwing, and any deflection (lower than a limit value) relative to thestable horizontal position introduces an aerodynamic moment of return.

Aerostats according to the invention can be placed at a stratosphericaltitude of, for example, 21 km above the ground.

The invention can be applied in particular for production of systems forlocation of mobile land, maritime or aeronautical units, in particularby differential measurement of the length of the radio-electric pathbetween the mobile units and aerostats according to the invention, orfor production of telecommunication systems, in particular formulti-media applications and communications with mobile units.

What is claimed is:
 1. A free aerostat, comprising: a strengtheningstructure (1, 3, 4, 5), which defines a shape which is symmetricalrelative to a main axis (2); at least one main chamber (16) closed in asealed manner, which is integral with the said structure, and ispressurised by a gas which is lighter than air, such as to permit flightof the aerostat; means (8, 9) for driving the aerostat comprising: oneor a plurality of particle-emission propulsion units (8) supported bythe said structure, which are regularly distributed around the main axis(2), and are designed to be able to drive the aerostat in rotation inone direction around the main axis (2), and to be able to be controlledfrom an active state to an inactive state and vice-versa, at least oncefor each rotation of the aerostat around the main axis (2); one or aplurality of mobile flaps (9), which are supported by the said structureoutside the main chamber (16), are distributed regularly around the mainaxis (2), and are designed to be able to be controlled at least once foreach rotation of the aerostat around the main axis (2), from an activestate, in which they brake the rotation of the aerostat, whilst exertingaerodynamic thrust which tends to displace the aerostat in translationperpendicularly relative to the main axis (2), to an inactive state, inwhich they do not offer any substantial resistance to the rotation ofthe aerostat, and vice versa; and on-board control means (19), which aredesigned to control the propulsion units (8) and the flaps (9) in orderto drive the aerostat in continuous rotation around the main axis (2);and drive the aerostat in translation, with at least one component whichis perpendicular to the main axis (2), relative to the volume of air inwhich it moves.
 2. An aerostat as claimed in claim 1, wherein it has anoverall axial dimension parallel to the main axis (2) which is smallerthan its overall radial dimension perpendicular to the main axis (2). 3.An aerostat as claimed in claim 2, wherein it has a general outer shapewhich is globally symmetrical in revolution around the main axis (2),and in particular is globally lenticular.
 4. An aerostat as claimed inclaim 1, wherein it comprises at least one propulsion unit (8) which isan ionic actuator.
 5. An aerostat as claimed in claim 1, wherein itcomprises at least propulsion unit (8) which is an air pulsation unit.6. An aerostat as claimed in claim 1, wherein it comprises at least oneflexible outer envelope (15), which delimits at least one main chamber(16) which is sealed against gases and is pressurised by a gas lighterthan air, and each of the mobile flaps (9) is disposed outside thisouter envelope (15).
 7. An aerostat as claimed in claim 6, wherein eachpropulsion unit (8) is secured to the structure (1, 3, 4, 5) inside theenvelope (15), and has a particle-ejection nozzle (10), which passes ina sealed manner through the envelope (15).
 8. An aerostat as claimed inclaim 1, wherein it comprises an on-board energy source (21, 18) whichis designed to assure the energy supply at least of each propulsion unit(8).
 9. An aerostat as claimed in claim 8, wherein the energy source(21, 18) comprises: photovoltaic solar cells (21) which are disposed onat least one upper surface portion (17) of the aerostat; and means (18)for storage of electrical energy.
 10. An aerostat as claimed in claim 1,wherein the on-board control means (19) are designed such that, in afirst angular sector (28) which extends from one side in a radialdirection (Da) perpendicular to the main axis (2), and is fixed inrelation to the relative wind (independently from the rotation of theaerostat around the main axis (2)), each propulsion unit (8) is in theactive state and each flap (9) is in the inactive state, whereas in asecond angular sector (29) which extends from the other side of thisradial direction (Da), each propulsion unit (8) is in the inactivestate, and each flap (9) is in the active state, such that the aerostatis driven in translation in relation to the relative wind, at leastsubstantially according to this radial direction (Da).
 11. An aerostatas claimed in claim 1, wherein the drive means (8, 9) are designed to beable to drive the aerostat in rotation at a speed ω of between 1 rd/sand 100 rd/s.
 12. An aerostat as claimed in claim 11, wherein the speedω is approximately 2πrd/s.
 13. An aerostat as claimed in claim 1,wherein each propulsion unit (8) and each flap (9) is designed to beable to be controlled from the inactive state to the active state, andfrom the active state to the inactive state in a period of less than2π/4ω, ω being the speed of rotation of the aerostat expressed inradians per second.
 14. An aerostat as claimed in claim 1, wherein itcomprises means for location of the position of the main axis (2)relative to a reference point which is fixed in relation to the ground,and means for location relative to this fixed reference point for theangular position of the structure (1, 3, 4, 5) relative to the main axis(2), and the said control means (19) comprise calculation means whichare designed to determine the control signals to be applied to eachpropulsion unit (8) and to each flap (9), according to signals issued bythese location means, and in accordance with a predetermined instructionsignal for the horizontal position and/or the horizontal path of themain axis (2), relative to the fixed reference point.
 15. An aerostat asclaimed in claim 1, wherein each of the propulsion units (8) isassociated with a peripheral portion (3, 4) of the structure (1, 3, 4,5) which is furthest away from the main axis (2), and is disposed suchas to exert a drive force which is at least substantially tangential.16. An aerostat as claimed in claim 1, wherein each of the flaps (9) isassociated with a peripheral portion (3, 4) of the structure (1, 3, 4,5) which is furthest away from the main axis (2), and is disposed suchas to exert a force which is at least substantially tangential.
 17. Anaerostat as claimed in claim 1, wherein the structure (1, 3, 4, 5)comprises a peripheral toric balloon (3), which is sealed against gasesand is over-pressured by a gas lighter than air, to a pressure greaterthan that of the main chamber (16), it comprises the same number ofpropulsion units (8) as flaps (9), and it comprises support parts (4)which are secured to this toric balloon (3), and are regularlydistributed around the main axis (2), each support part (4) supportingat least one propulsion unit (8) and/or at least one mobile flap (9).18. An aerostat as claimed in claim 1, wherein the structure (1, 3, 4,5) comprises: a rigid, globally cylindrical hollow central core (1),which can enclose the electronic and/or computer and/ortelecommunications and/or energy storage equipment, and/or equipment ofan on-board mission; an over-pressurised peripheral toric balloon (3);support parts (4) which are secured to the peripheral toric balloon (3),and support the propulsion unit(s) (8) and the mobile flap(s) (9);connection means (5), which connect the central core (1) and the supportparts (4); and an outer envelope (15), which surrounds and/or completesthe volume delimited by the peripheral toric balloon (3) and the centralcore (1), in order to circumscribe at least one pressurised, sealed mainchamber (16).
 19. An aerostat as claimed in claim 1, wherein each mobileflap (9) extends at least substantially radially, and is mobile parallelto the main axis (2), between a position retracted in a flap compartment(11), in which it does not interfere with the relative current of airobtained from displacements of the aerostat relative to the volume ofair in which it is placed, and a deployed position, in which itinterferes with the current of air, and tends to brake the rotation ofthe aerostat around the main axis (2).
 20. An aerostat as claimed inclaim 1, wherein the gas consists of helium, and the volume of the mainchamber (16) is designed to permit stratospheric flight of the aerostat.21. An aerostat as claimed in claim 1, wherein it has an overall radiusof between 5 m and 50 m, in particular of approximately 15 m, and anoverall axial height of between 1 m and 20 m, and in particularapproximately 10 m.